Cross-compiling LibreOffice
===========================

Notes on cross-compiling LibreOffice, written by Tor Lillqvist
<tlillqvist@novell.com> <tml@iki.fi> in May, 2011.

Cross-compilation of LibreOffice is not possible yet. Some initial
work is done, "baby steps", but a lot remains. This work is highly
experimental and done mostly in my own spare time just for the hacking
pleasure. No promise, explicit or implied, is given that it will ever
be finished.

Searching for information about cross-compilation of OpenOffice.org
(the predecessor of LibreOffice) you will find information about what
actually was not cross-compilation, but using QEMU.

The cross-compilation experimentation is going on for three platforms:
Windows, iOS and Android. This work is being done on the master branch
of LibreOffice. Some other people have talked about setting up a
separate branch for Android work, or even separate clones at github. I
am not interested in that.


General
-------

In GNU Autoconf terminology, "build" is the platform on which you are
running a build on some software and "host" is the platform on which
the software you are building will run. Only in the specific case of
building compilers and other programming tools is the term "target"
used to indicate the platform for which the tools your are building
will produce code. As LibreOffice is not a compiler, the "target" term
should not be used in the context of cross-compilation.

(For a case where all three of "build", "host" and "target" are
different: consider a gcc cross-compiler running on Windows, producing
code for Android, where the cross-compiler itself was built on
Linux. (This is a real case.) An interesting tidbit is that such
configurations are called "Canadian Cross".)

Even though the LibreOffice build mechanism is highly unorthodox, the
configure script takes the normal --build and --host options like any
GNU Autoconf -based configure script. To cross-compile, you basically
need just to specify a suitable --host option and things should work
out nicely. In practise, some more details might be needed. See
examples below.


What is so hard, then?
----------------------

Despite the fact that the configure script takes normal --build and
--host options, that is just the beginning. In practise a lot of work
was necessary to separate tests for "host" and "build" platforms in
the configure script. See the git log for details. And the reasonably
"standard" configure.in is just the top level; when we get down to the
actual makefilery used to build the bits of LibreOffice, it gets much
worse.


Windows
-------

There is some support in LibreOffice already (from OpenOffice.org) for
building it locally on Windows but with the GNU tool-chain, i.e. what
is commonly known as MinGW. But as far as I know, that work has never
attempted cross-compilation.

This OOo-originated MinGW support attempts to support both running
Cygwin gcc in its -mno-cygwin mode, and a native MinGW compiler.  The
-mno-cygwin mechanism in the Cygwin gcc is rapidly being obsoleted, if
it isn't already, and I have not attempted to check that it keeps
working. Ditto for native MinGW; if one compiles natively on Windows,
why not use Microsoft's compiler, as OOo/LO has been build for Windows
all the time using that and it works fine. In my opinion, it makes
sense to use MinGW only for cross-compilation. (Because of obvious
benefits like speed improvement, easier automation in systems like the
openSUSE Build Servce, etc.)

MinGW is available as cross-build toolchains pre-packaged in more or
less official packages for many Linux distros including Debian, Fedora
and openSUSE. Personally I use the mingw32 packages in the openSUSE
Build Service, running on openSUSE.

It is somewhat unclear how well thought-out the conditionals and code
for MinGW inside the LibreOffice code actually is. The little I have
seen of it seems a bit randomish, with copy-pasting haveing been
preferred to factoring out differences.

The autogen.lastrun I use for my MinGW cross-compilation experimentation is:

CC=ccache i686-w64-mingw32-gcc
CXX=ccache i686-w64-mingw32-g++
CC_FOR_BUILD=ccache gcc
CXX_FOR_BUILD=ccache g++
--build=x86_64-unknown-linux-gnu
--host=i686-w64-mingw32
--with-distro=LibreOfficeWin32
--disable-build-mozilla
--disable-ext-nlpsolver
--disable-ext-pdfimport
--disable-ext-presenter-console
--disable-ext-presenter-minimizer
--disable-ext-report-builder
--disable-ext-scripting-beanshell
--disable-ext-scripting-javascript
--disable-ext-wiki-publisher
--disable-ext-wiki-publisher
--disable-mozilla
--disable-zenity
--with-external-tar=/mnt/hemulen/ooo/git/master/src
--with-num-cpus=1
--with-max-jobs=1
--with-system-altlinuxhyph
--with-system-boost
--with-system-curl
--with-system-db
--with-system-expat
--with-system-hunspell
--with-system-icu
--with-system-jpeg
--with-system-lpsolve
--with-system-neon
--with-system-openssl
--with-system-redland
--with-system-libwpd
--with-system-libwps
--with-system-libwpg
--with-system-libxml
--with-system-libxslt
--with-system-mythes
--with-system-python
--with-system-zlib
--with-vendor=no


iOS
---

iOS is the operating system of Apple's mobile devices. Clearly for a
device like the iPad it would be totally unacceptable to run a normal
LibreOffice application with a overlapping windows and mouse-oriented
GUI widgets. No work has been done (at least publicly) to design a
touch GUI for LibreOffice, so the work on cross-compiling LibreOffice
for iOS is extremely experimental, and of course partly pointless;)
But it is interesting and fun nonetheless.

Obviously it will make sense to build only a part of LibreOffice's
code for iOS. Most likely all GUI-oriented code should be left out,
and some iOS app that eventually wants to use the remaining bits will
handle all its GUI in a platform-dependent manner. How well it will be
possible to do such a split remains to be seen. As I said, this is
highly experimental and just in its baby steps phase.

Technically, one important special aspect of iOS is that apps are not
allowed to load own dynamic libraries. (System libraries are used in
the form of dynamic libraries, just like on MacOSX, of which iOS is a
variant.) So all the libraries in LibreOffice that normally are shared
libraries (DLLs on Windows, shared objects (.so) on Linux, dynamic
libraries on MacOSX (.dylib)) need to be built as static archives
instead. Obviously this will have some interesting consequences for
how UNO is implemented and used. None of that has been spared much
thought yet.

The Apple tool-chain for iOS cross-building is available only for
MacOSX, so that is where I have been doing it.

Here is my autogen.lastrun for iOS:
CXX=ccache /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/g++-4.2 -arch armv7 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
CC=ccache /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/gcc-4.2 -arch armv7 -isysroot /Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS4.3.sdk
CC_FOR_BUILD=ccache /Xcode3/usr/bin/gcc-4.0
CXX_FOR_BUILD=ccache /Xcode3/usr/bin/g++-4.0
--with-distro=LibreOfficeiOS
--with-external-tar=/Volumes/ooo/git/master/src
--with-icu-native-build-root=/Users/tml/lo-macosx/icu/unxmacxi.pro/misc/build/icu/source
--with-num-cpus=1
--with-max-jobs=1


Android
-------

I don't know much about Android, but from a technical point of view it
is a kind of Linux, of course. As far as I know it is allowed for an
Android app to use shared objects, but if it isn't, then just the same
approach as used on iOS will need to be used.

As for the GUI, the same holds as said above for iOS.

I have done my Android cross-compilation work on Linux (openSUSE in
particular), but it could as well be done on MacOSX. The Android
cross-buld tool-chain (the "Native Development Kit", or NDK) is
available for Linux, MacOSX and Windows. (Trying to cross-compile from
Windows will probably drive you insane.)

Here is my autogen.lastrun for Android:
CC=ccache /home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gcc --sysroot /home/tml/android-ndk-r5b/platforms/android-9/arch-arm
CXX=ccache /home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-g++ --sysroot /home/tml/android-ndk-r5b/platforms/android-9/arch-arm
AR=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ar
NM=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-nm
OBJDUMP=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-objdump
RANLIB=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-ranlib
STRIP=/home/tml/android-ndk-r5b/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-strip
CC_FOR_BUILD=ccache gcc
CXX_FOR_BUILD=ccache g++
--build=x86_64-unknown-linux-gnu
--disable-zenity
--with-distro=LibreOfficeAndroid
--with-external-tar=/mnt/hemulen/ooo/git/master/src


That's all, thank you, and have a nice day. People with commit access,
feel free to edit this document and add yourself below. Sorry for
writing now initially from such a personal point of view.

--Tor Lillqvist <tlillqvist@novell.com>, <tml@iki.fi>